depends: be sure our staging libs are first in the link-path
depends: don't add sdk paths for osx, toolchain defaults pick them up
depends: use -search_paths_first when linking on darwin

Otherwise local shared libs will be picked up before our built static
ones
depends: nuke the libssh shared libs for darwin too
depends: fix librtmp's install_name
depends: add the missing darwin module for python
depends: fix broken pyo sources in darwin
depends: fix xcode project so that it links properly with static libs
depends: fix debug xcode build for static libs
depends: temp fix for python linker error on ios
depends: add dummy file for iconv test